As a means for transporting a medicament specifically to a pathological lesion, methods of encapsulating a medicament in liposomes have been proposed. In particular, in the field of therapeutic treatments of malignant tumors, many reports have been made as for effectiveness of liposomes encapsulating an antitumor agent. Further, a multifunctional envelope-type nano device (MEND: henceforth sometimes abbreviated as “MEND” in the specification, see, for example, Drug Delivery System, 22-2, pp. 115-122, 2007 and the like) has been proposed. This structure can be used as a drug delivery system for delivering a gene or the like selectively into particular cells, and is known to be useful for, for example, gene therapy of tumors and the like.
Variety of methods have been proposed for modifying the surface of a lipid membrane structure with a functional molecule, as means for delivering an objective substance such as medicaments, nucleic acids, peptides, polypeptides, and saccharides to specific parts such as target organs and tumor tissues using a lipid membrane structure. When a lipid membrane structure encapsulating a medicament such as antitumor agent reaches a target cell, the structure is taken up into the cell by endocytosis and enclosed in the endosome. Then, the structure releases the encapsulated medicament into the cytoplasm due to hydrolytic action of an enzyme in the lysosome or the like. In order to enhance the release of medicament from a liposome taken up into the endosome, a liposome has been proposed of which surface is modified with a peptide, GALA (Biochemistry, 26, pp.2964-2972, 1987for the peptide (SEQ ID NO: 13); Biochemistry, 43, pp.5618-5623, 2004for the liposome) and MEND (Japanese Patent Unexamined Publication (KOKAI) No. 2006-28030).
Further, as means for localization of a lipid membrane structure encapsulating an objective substance such as nucleic acid into the nucleus of a target cell, there have been proposed, for example, a liposome of which outer surface is modified with octaarginine (SEQ ID NO: 4) (International Patent Publication WO2005/32593; Journal of Controlled Release, 98, pp.317-323, 2004), a bilamellar liposome having a lipid membrane modified with a nucleus permeable peptide (International Patent Publication WO2006/101201), and a liposome of which surface is modified with a monosaccharide such as galactose and mannose (International Patent Publication WO2007/102481). It has been reported that a multilamellar lipid membrane structure (T-MEND) modified with a monosaccharide has fusability with a lipid membrane and a nuclear membrane, and is capable of improving gene expression efficiency as an experimental result in vitro.
If a nucleic acid encoding an antigenic protein can be introduced into the nucleus of an immunocyte, especially dendritic cell having an antigen-presenting action, a protein transcribed and translated from the nucleic acid in the dendritic cell can be presented as an antigen on the surface of the dendritic cell, and the host organism can acquire immunity against that protein. From such point of view, a technique for efficiently delivering a nucleic acid into the nucleus of immunocyte, such as dendritic cell has been desired.
However, where a nucleic acid is introduced into the nucleus of dendritic cell by using a lipid membrane structure such as the aforementioned MEND, the nucleic acid introduction efficiency is insufficient compared with introduction into other cells, for example, tumor cells and hepatic parenchymal cells. Before an introduced nucleic acid is finally expressed in the nucleus, the nucleic acid inevitably undergoes various intracellular kinetic processes such as uptake into cell, escape from endosome, migration into nucleus, and intranuclear transcription. However, in nondividing cells such as dendritic cell, an intact double-layered nuclear membrane constantly exist, and it is estimated that this nuclear membrane inhibits the intranuclear migrating ability of the lipid membrane structure. Therefore, in order to deliver a nucleic acid into the nucleus of dendritic cell by using a lipid membrane structure, it is a very important object how the nucleic acid successfully overcomes each of the aforementioned processes, especially, the barrier of the double-layered nuclear membrane.
In addition, a polypeptide consisting of 30 amino acid residues called KALA peptide (SEQ ID NO: 5) is known, and it has been reported that the peptide can form a complex with a plasmid DNA using cationic charge of itself (Biochemistry, 36, pp.3008-3017, 1997). However, this reference fails to suggest whether or not this peptide promotes intranuclear migration of a lipid membrane structure.